Many database management systems, including relational database management systems that process structured-query-language (“SQL”) queries, compile queries submitted to the database management system into an intermediate form, optimize the intermediate forms, and instantiate the compiled queries to produce query plans that are executed by a query-processing engine to store data and modify data already stored in the database management system and to retrieve data from the database management system. Query compilation and compiled-and-optimized-query instantiation are relatively straightforward operations, but query optimization can be computationally expensive. In order to decrease computational overheads and increase the rate of query processing, certain database management systems store compiled and optimized queries, or optimized query plans, in a memory cache, using a process referred to as “query-plan caching,” so that cached optimized query plans may be matched to subsequently received queries, retrieved from cache, and reused to avoid the expense of carrying out compiled-query optimization. Unfortunately, the process of matching subsequently received queries to cached optimized query plans may be difficult mid inaccurate, as a result of which subsequently received queries may be inadvertently matched with inappropriate and non-optimal cached query plans, in turn leading to query-processing efficiencies and in worst cases, degradation in query-processing throughput and computational efficiencies with respect to database management systems that do not cache optimized query plans. Researchers and developers working in the field of database management systems, manufacturers and vendors of database management systems and associated hardware, and ultimately, users of database management systems continue to seek improved methods and systems for optimized-query-plan caching in order to achieve greater efficiencies in query processing.